AI's learned their style through RLHF, with semi-focused, partially motivated humans giving feedback on short(ish)-form content.

For the most part, Modelese is the revealed preference of the average, not-heavily-invested human. This doesn't fully explain the Claudish coming from Opus 5 and Fable (this seems like it may be due to excessive RLVR or RLAI), but yeah.

It's got a lot of cheap writing tricks that make people think it's smart and helpful.